1. Field of the Invention
This invention relates to multi-conductor electrical cables of the type used in oilfield wireline logging cables.
Once an oil well is drilled, it is common to log certain sections of the well with electrical instruments. These instruments are referred to as "wireline" instruments, as they communicate with the logging unit at the surface of the well through an electrical wire or cable with which they are deployed. Such cables are used for transmitting power and for telemetry. Since down hole temperatures and pressures can reach, for example, 500.degree. F. and sometimes up to 25,000 psi, the cables must be designed to withstand extreme environmental conditions.
2. Description of the Related Art
A standard cable in the oilfield industry is a seven-conductor design called a "heptacable." As shown in FIG. 1, the heptacable 2, generally 0.38-0.55 inches in diameter, includes six conductors 4 symmetrically wrapped around a center conductor 6. These types of heptacables are used extensively in the oilfield wireline logging industry, for the purpose of lowering and retrieving sensors and instruments capable of measuring acoustic, nuclear, resistivity, and nuclear magnetic resonance (NMR) properties of freshly drilled downhole rock formations and their fluid content. Other uses of the heptacable include cement analysis, perforating, PVT and fluid sampling, and other electro-mechanical services that may be required in oil and gas wells.